Body core temperature is universally accepted as an important indicator of the physical condition of humans and other warm blooded animals.
For many years, the most common and traditional method of determining body core temperature was to insert a traditional contact-type thermometer, such as a mercury-in-glass thermometer or an electronic pencil thermometer, into a body orifice of a patient, such as into the mouth or rectum of a patient. As known in the art, a traditional contact-type thermometer includes a probe with a thermal temperature sensor that responds to the temperature of an object, i.e., the surface of a body orifice, with which the sensor is placed in contact. The rate of response of the sensor depends on the degree of thermal coupling between the sensor and the surface, the physical characteristics of the surface, the isolation of the sensor from other components in the thermometer and the thermal capacity of the sensor.
Traditional contact-type thermometers typically determine body core temperature in accordance with either the equilibrium technique or the predictive technique. In the equilibrium technique, the sensor of the thermometer needs to remain inserted, and typically be maintained in contact with a surface, in the mouth, rectum or other body orifice of a patient for a relatively long time. A long contact interval is required because the contact-type thermometer relies upon the conduction of heat to the sensor to determine body core temperature. The sensor remains in contact with the surface until the sensor stabilizes its response, such that the respective temperatures of the sensor and the surface become nearly equal. Although a contact-type thermometer operating in accordance with the equilibrium technique will provide an accurate indication of body core temperature, the temperature measurement process is slow and also uncomfortable for a patient.
In a traditional contact-type thermometer that determines body core temperature in accordance with the predictive technique, the sensor of the thermometer is inserted into the body for a short period of time which is not long enough for the respective temperatures of the sensor and contact surface to become nearly equal. During the time that the sensor is inserted into the body orifice, the rate of response of the sensor is measured. The measured rate of response is then used to mathematically estimate the temperature at which the sensor and surface would have become equal had the sensor and the surface been maintained in contact with each other for a sufficiently long time. Accordingly, the predictive technique determines body core temperature of a patient without requiring that the sensor be maintained in contact with the patient until the sensor achieves an equilibrium temperature. As known in the art, some contact-type thermometers rely on software data processing, while others rely on a hardware design to determine body core temperature in accordance with the predictive technique. For example, in one prior art traditional contact-type thermometer a hardware integrator is used to estimate the equilibrium temperature of a slow responding thermistor of the thermometer. Although the predictive technique provides for a much quicker determination of body core temperature than the equilibrium technique, the equilibrium technique provides for greater accuracy in the determination of body core temperature than the predictive technique.
The prior art also includes thermometer apparatuses that determine body core temperature based on the detection of infrared (“IR”) energy signal emissions from the tympanic membrane or ear canal of a patient. In operation of a typical IR thermometer, an IR sensor that takes a reading of IR energy, and any associated sensing elements in the IR thermometer, are not required to be inserted into, or placed in contact with a surface of, a body orifice of a patient. The determination of body core temperature based on an IR energy reading, thus, avoids the need to insert a probe into a body orifice of a patient. In addition, IR thermometers can determine body core temperature within a few seconds. Further, some IR thermometers determine body core temperature based on measurements of skin temperature obtained from detection of IR energy emission and ambient temperature.
IR thermometers, however, have several drawbacks. The accuracy and operability of an IR thermometer depend on the operator's technique in positioning the thermometer to detect an IR energy signal. Also, ambient temperature, and the cleanliness of an IR lens within the IR thermometer, can affect the accuracy and operability of an IR thermometer. Further, the components included in a typical IR thermometer are relatively expensive, such that an IR thermometer constitutes a relatively costly device.
Therefore, a need exists for a thermometer apparatus for determining body core temperature which is easy and relatively inexpensive to manufacture, provides for a relatively quick determination of body core temperature, has an accuracy and operability that does not depend an operator technique, requires only minimal contact with the patient and does not require insertion of a portion of the apparatus into a body orifice of a patient.